For the conversion means of solar systems used for generating energy such as electrical or thermal energy, their production depends on the incident solar irradiation to which they are exposed (referred to below as irradiation). A typical solar panel produces electrical energy which varies with the sunlight and brightness of the environment around the panel.
Forecasting the irradiation of a solar system enables anticipating the amount of energy that will be produced over a future time horizon. There are different approaches to forecasting the irradiation of such a system, including:                forecasts using meteorological models (forecast horizon ranging from several hours to several days);        forecasts based on irradiation measurements taken by a measurement instrument on the ground (such as a pyranometer), mathematical models being used to predict the values of upcoming measurements on the basis of historical measurements (forecast horizon ranging from a few minutes to several hours);        forecasts by processing satellite images, and estimating the solar radiation received at ground level from satellite data (forecast horizon of several minutes to several hours);        forecasts using images of the sky taken from the ground, to determine the movement of cloud cover and thus deduce the irradiation on the ground (forecast horizon of up to several minutes).        
With the latter approach, i.e. forecasting by processing images of the sky taken from the ground, estimating and forecasting solar radiation on the ground can be done with good accuracy, either in real time or on the basis of an approaching forecast horizon (5 to 15 minutes for example). “Forecast horizon” is understood to mean the time interval between the moment the forecast is made and the moment when the expected event occurs.
Generally, forecasts based on images of the sky taken from the ground comprise at least three phases, which are:                locating a masking cloud cover,        estimating the motion of the masking cloud cover, and        determining the solar radiation at ground level based on the one or more masking cloud covers detected and their estimated movements.        
During the first phase, the presence of a masking cloud cover is conventionally recognized from an image taken in an area of interest (typically near solar panels). From the location of the masking cloud cover in the image, a cloud cover index for the area of interest can be calculated.
In the second phase, the movement of the detected masking cloud cover or masks is analyzed.
Thirdly, the images are translated into ground-level radiation values based on the detected cloud covers and their movements. To this end, processing methods that are known per se can be used to convert the luminous intensity of each pixel (pixel value) of the images, into a raw ground level irradiation value. For illustrative purposes, one of the possible processing methods is disclosed in patent US20100309330.
However, it turns out that cloud covers are usually considered as impacting the radiation at ground level regardless of their position relative to the area of interest. A cloud cover which is at the earth's horizon relative to the area of interest, however, does not have the same influence on the ground-level irradiation received as would other cloud cover at the zenith for example. A cloud cover at zenith has pixels that more directly impact the ground-level radiation received. Significant differences can thus appear between the value of the estimated or predicted ground-level radiation and the irradiation actually received in the area of interest.
These differences skew the estimation and forecast of the energy production of solar systems, and as a result adversely affect the optimization of energy management (in this case with an incorrect assessment of the amount of energy actually produced and/or to be produced by other production devices to compensate).
There is therefore a need to develop a more accurate method of estimating and forecasting the energy production of a solar system.
The invention improves the situation in this regard.